Recovery of 1,2-dichloroethane from vinyl chloride production effluent

ABSTRACT

An effluent from a process for producing vinyl chloride includes 1,2-dichloroethane and heavier components, with the 1,2-dichloroethane being recovered, in a heavy ends stripping column by use of ethane and/or ethylene as stripping gas. The stripping gas is ultimately used for production of vinyl chloride.

This invention relates to the production of vinyl chloride, and moreparticularly to a new and improved process for recovering chlorinatedhydrocarbons from an effluent produced in a process directed to theproduction of vinyl chloride.

In a process for producing vinyl chloride, the effluent includes1,2-dichloroethane and higher boiling chlorinated hydrocarbons. The1,2-dichloroethane is generally separated from the higher boilingchlorinated hydrocarbons in a heavy ends distillation column in which1,2-dichloroethane is recovered as overhead. In most cases, the bottomsfrom the heavy ends column includes varying amounts of1,2-dichloroethane and as a result, various processes have been proposedfor further treating the bottoms from the heavy ends distillation columnin order to recover 1,2-dichloroethane therefrom; e.g., U.S. Pat. No.3,634,200. The necessity to provide for further treatment of the bottomsfrom the heavy ends column to maximize recovery of 1,2-dichloroethaneadds to the capital and operating expense of the plant and, accordingly,there is a need for improved methods for recovering 1,2-dichloroethanefrom higher boiling (heavier)components.

Accordingly, the principle object of the present invention is to providea new and improved process for recovering 1,2-dichloroethane fromheavier materials produced in a process directed to the production ofvinyl chloride.

In accordance with the present invention, there is provided a processfor producing vinyl chloride wherein ethane and/or ethylene arechlorinated to produce a reaction effluent containing vinyl chloride,1,2-dichloroethane and chlorinated hydrocarbons heavier than1,2-dichloroethane. Vinyl chloride is recovered from the effluent and1,2-dichloroethane is stripped from the heavier chlorinated hydrocarbonsby use of a stripping gas which contains ethane and/or ethylene, withthe stripped 1,2-dichloroethane being dehydrochlorinated to vinylchloride. The invention will be further described with respect to thepreferred embodiment in which a molten salt is employed for thechlorination of ethane and/or ethylene, but as hereinafter described,the broader aspects of the present invention are not limited to such apreferred technique.

More particularly ethane and/or ethylene is contacted with a meltcomprising a multivalent metal chloride in its higher and lower valencestate, either with or without hydrogen chloride and/or chlorine as achlorinating agent, preferably with chlorine and/or hydrogen chloride,to produce a reaction effluent comprising vinyl chloride,1,2-dichloroethane and chlorinated hydrocarbons heavier than1,2-dichloroethane. As hereinafter described, the reaction effluent mayalso include other components such as ethyl chloride, ethane, ethylene,etc.

The reaction effluent is then introduced into a separation and recoverysection wherein components lighter (lower boiling) than1,2-dichloroethane are separated from the effluent; i.e., vinylchloride, ethyl chloride, ethane, ethylene. The remaining effluentcontains 1,2-dichlorethane and chlorinated hydrocarbons heavier than1,2-dichloroethane (higher boiling than 1,2-dichloroethane) which may beone or more of the following: trichloroethane, tetrachloroethane,tetrachloroethylene, or trichloroethylene. The heavier components mayfurther include chlorinated butanes and/or butenes and tars. Inaccordance with the present invention, the stream containing1,2-dichloroethane and heavier chlorinated hydrocarbons is introducedinto a stripping zone wherein 1,2-dichloroethane is stripped therefromby use of a stripping gas containing ethane, ethylene or mixturesthereof. The ethane and/or ethylene used in the stripping gas may befresh feed or, hereinafter described, the ethane and/or ethylene may bea recycle gas from the process. It is also to be understood that thestripping gas can include components in addition to ethane and/orethylene; in particular an inert gas, such as nitrogen.

The stripper for stripping 1,2-dichloroethane from heavier components isoperated at temperatures and pressures which are effective forseparating 1,2-dichloroethane from the heavier components. In general,the stripper is operated at an overhead temperature from about 225° toabout 350°F, preferably an overhead temperature from about 280° to about310°F, a bottoms temperature from about 270° to about 410°F, preferablyfrom about 325° to about 360°F and a pressure from about 20 psig toabout 130 psig, preferably from about 55 psig to about 80 psig.

The stripping gas is preferably introduced into the bottoms reboiler ofthe stripper, whereby the partial pressure of 1,2-dichloroethane overthe heavy residue is reduced and the stripping gas is heated. Thestripping gas is preferably introduced in an amount to provide a moleratio of stripping gas to vapor generated in the bottoms reboiler offrom 0.5:1 to 1.5:1.

The 1,2-dichloroethane stream recovered from the stripper, which alsoincludes ethane and/or ethylene used as stripping gas, is thenintroduced into a dehydrochlorination reaction zone to effectdehydrochlorination of 1,2-dichloroethane to vinyl chloride. Thedehydrochlorination may be effected by a conventional thermal orcatalytic process or by the use, as hereinafter described, of a moltensalt mixture containing the higher and lower valent forms of amultivalent metal chloride. The dehydrochlorination reaction effluent isthen introduced into a separation and recovery zone for recovery of thevarious components.

Accordingly, in accordance with the present invention, separation of1,2-dichloroethane from heavier components is maximized by using ethaneand/or ethylene as a stripping gas. The recovered 1,2-dichloroethaneoverhead, which includes the stripping gas, is subjected todehydrochlorination. The ethane and/or ethylene used as stripping gasmay be partially chlorinated in the dehydrochlorination zone, ashereinafter described, and in any event, the ethane and/or ethylene orchlorinated product(s) produced therefrom are ultimately utilized in theproduction of vinyl chloride.

As hereinabove noted the melts employed in the chlorination include thehigher and lower valent forms of a chloride of a multivalent metal;i.e., a metal having more than one positive valence state, such asmanganese, iron copper, cobalt and chromium, preferably copper. In thecases of higher melting multivalent metal chlorides, such as copperchlorides, a metal salt melting point depressant which is non-volatileand resistant to the action of oxygen at the process conditions, such asa chloride of a univalent metal, i.e., a metal having only one positivevalence state, is added to the multivalent metal chloride to form amolten salt mixture having a reduced melting point. The univalent metalchlorides, are preferably alkali metal chlorides, such as potassium andlithium chlorides in particular, but it is to be understood that othermetal chlorides and mixtures thereof, such as the heavy metal chlorides,i.e., heavier than copper, of Groups I, II, III and IV of the PeriodicTable; e.g., zinc, silver, and thallium chloride, may also be employed.The metal chloride melting point depressant is added in an amountsufficient to maintain the salt mixture as a melt at the reactiontemperatures, and is generally added in an amount sufficient to adjustthe melting point of the molten salt mixture to a temperature of belowabout 500°F. In the case of a salt mixture of copper chlorides andpotassium chloride, the composition of the melt ranges between about 20and about 40%, preferably about 30%, by weight, potassium chloride, withthe remaining being copper chlorides. It is to be understood, however,that in some cases the catalyst melt may have a melting point higher500°F., provided the catalyst remains in the form of the melt throughoutthe processing steps. It is further to be understood that the melt maycontain a mixture of multivalent metal chlorides or other reactionpromoters. It is also to be understood that in some cases, metalchloride may be maintained as a melt without the addition of a univalentmetal halide.

The chlorination reaction sequence for converting ethane and/or ethyleneto vinyl chloride, using copper chloride as a representative example, isbelieved to be represented by the following equations:

    (1) 2CuCl.sub.2 → 2 CuCl + Cl.sub.2

    (2) C.sub.2 H.sub.6 + CL.sub.2 → C.sub.2 H.sub.5 Cl+HCl

    (3) C.sub.2 H.sub.4 +Cl.sub.2 → C.sub.2 H.sub.4 Cl.sub.2

    (4) C.sub.2 H.sub.4 Cl.sub.2 → C.sub.2 H.sub.3 Cl+HCl

    (5) C.sub.2 H.sub.5 Cl → C.sub.2 H.sub.4 Cl.sub.2 +HCl

    (6) C.sub.2 H.sub.5 Cl+Cl.sub.2 → C.sub.2 H.sub.4 Cl.sub.2 +HCl

    (7) C.sub.2 H.sub.4 Cl.sub.2 → C.sub.2 H.sub.3 CL+HCl

It should be apparent from the hereinabove described reaction sequence,as represented by the above equations, that there is a continuousdepletion of the higher valent metal chloride; i.e., cupric chloride,and a net production of hydrogen chloride. Therefore, if the process isto be effected on a continuous basis, a provision must be made forregeneration of the cupric chloride and disposal of the hydrogenchloride.

In accordance with the preferred embodiment of the invention, the meltcontaining the multivalent metal chloride, in both its higher and lowervalence state, may be initially contacted in a separate reaction zonewith an oxygen-containing gas to produce the oxychloride of the metal,and the melt, now also containing the oxychloride of the multivalentmetal, is then contacted in a chlorination zone with chlorine and/orhydrogen chloride and the feed containing ethane and/or ethylene toproduce vinyl chloride and dichloroethane. The reaction between the meltand the oxygen-containing gas, using copper chloride as a representativemultivalent metal chloride, is represented by the following equation:

    (8) 2CuCl + 1/2 O.sub.2 → CuO. CuCl.sub.2

The copper oxychloride then reacts with the hydrogen chloride generatedduring the production of the vinyl chloride as represented by thefollowing equation:

    (9) CuO.CuCl.sub.2 + 2HCl → 2CuCl.sub.2 + H.sub.2 O

thus, in accordance with this embodiment, there is no net production ofhydrogen chloride and no net depletion of cupric chloride, and in fact,in order to operate the process on a continuous basis, chlorine and/orhydrogen chloride must be added to the system as represented by thefollowing overall equations:

    (10) C.sub.2 H.sub.6 + 1/2Cl.sub.2 + 3/4O.sub.2 → C.sub.2 H.sub.3 Cl + 3/2 H.sub.2 O

    (11) c.sub.2 h.sub.6 + hcl + O.sub.2 → C.sub.2 H.sub.3 Cl + 2 H.sub.2 O

    (12) c.sub.2 h.sub.4 + 1/2cl.sub.2 + 1/4O.sub.2 → C.sub.2 H.sub.3 Cl + 1/2 H.sub.2 O

    (13) c.sub.2 h.sub.4 + hcl + 1/2 O.sub.2 → C.sub.2 H.sub.3 Cl + H.sub.2 O

the hydrogen chloride and/or chlorine may be added to the system eitherwith the oxygen containing gas or in the chlorination zone with theethane and/or ethylene feed, preferably with the ethane and/or ethylenefeed so as to eliminate the necessity of providing means for recoveringhydrogen chloride and/or chlorine from the gaseous effluent from theoxygen-contacting step. In addition, the additions of chlorine and/orhydrogen chloride with the ethane and/or ethylene feed improves theyield of vinyl chloride.

In accordance with another embodiment of the invention, the oxygencontaining gas may be introduced into the chlorination zone with theethane and/or ethylene feed to produce the oxychloride of themultivalent metal, in situ, but such a procedure is not preferred inthat there may be a loss of ethane and/or ethylene feed by combustion.In addition, the quantities of oxygen and ethane and/or ethylene wouldhave to be regulated to prevent explosive compositions.

In accordance with a further embodiment of the invention, the highervalent metal chloride may be regenerated by contacting the melt with achlorine-containing gas, such contacting being effected eithersimultaneously with the production of vinyl chloride and dichloroethanefrom the ethane and/or ethylene feed or in a separate reaction zone. Theregeneration of the higher valent multivalent metal chloride, usingcopper chloride as a representative example, may be represented by thefollowing equation:

    (14) 2CuCl + Cl.sub.2 → 2CuCl.sub.2

and the overall reaction, using ethylene as a representative feed, bythe following equation:

    (15) C.sub.2 H.sub.4 +Cl.sub.2 → C.sub.2 H.sub.3 Cl + HCl

This procedure is not particularly preferred in that there is a netproduction of hydrogen chloride.

In accordance with still another embodiment of the invention, thehydrogen chloride generated during the production of vinyl chloride anddichloroethane in the chlorination zone may be recovered from thereaction effluent, and employed in a separate reaction zone, along withan oxygen-containing gas, to regenerate the higher valent metalchloride, as represented by the following equation:

    (16) 2HCl +2CuCl +1/2 O.sub.2 → 2CuCl.sub.2 + H.sub.2 O

this procedure is also less preferred in that provision must be made forrecovering the hydrogen chloride from the chlorination zone reactioneffluent.

Although several embodiments for the chlorination of ethane and/orethylene by the use of melts containing a multivalent metal chloride inboth its higher and lower valence state have been described, thepreferred embodiment for such chlorination involves contacting of themelt with molecular oxygen in a first reaction zone to provide a moltensalt mixture which further includes the oxychloride of the multivalentmetal, followed by circulating the melt from the first reaction zone toa second reaction zone(chlorination zone) wherein the melt is contactedwith ethane and/or ethylene and chlorine and/or hydrogen chloride toproduce a chlorinated effluent, including vinyl chloride anddichloroethane. This embodiment is preferred in that higher yields areobtained with the direct addition of chlorine and/or hydrogen chlorideinto the chlorination reactor.

The reaction effluent produced in the chlorination reactor is introducedinto a separation and recovery zone wherein vinyl chloride is recovered,as reaction product, and wherein 1,2-dichloroethane is stripped fromheavier components using a stripping gas which contains ethane and/orethylene. The stripped 1,2-dichloroethane which also includes ethaneand/or ethylene, used as stripping gas, is then dehydrochlorinated tovinyl chloride.

In accordance with one embodiment, the dichloroethane isdehydrochlorinated to vinyl chloride by contacting the dichloroethanewith a melt containing a multivalent metal chloride in both its higherand lower valence state, with the reaction being represented by thehereinabove equation (7):

    (7) C.sub.2 H.sub.4 Cl.sub.2 → C.sub.2 H.sub.3 Cl + HCl

The melt may also contain the oxychloride of the multivalent metalwhereby there is essentially no net production of hydrogen chloride, asrepresented by hereinabove equation (9):

    (9) 2HCl + CuO.CuCl.sub.2 → 2CuCl.sub.2 + H.sub.2 O

the use of the hereinabove described melts for the dehydrochlorinationof dichloroethane (in particular the 1,2-dichloroethane) to vinylchloride is particularly advantageous in that the melts direct thedehydrochlorination to the production of vinyl chloride at high rates ofconversion and high vinyl chloride selectivity. The 1,2-dichloroethane,which constitutes the major portions of the dichloroethane produced (insome cases essentially all of the dichloroethane product is1,2-dichloroethane), may be converted to vinyl chloride at conversionrates greater than 90%, while retaining vinyl chloride selectivity atgreater than 90%. It is to be understood, however, that although thedehydrochlorination of the present invention may be effectively operatedat conversions greater than 90%, for some operations, lower conversionrates may be employed. The ethane and/or ethylene introduced into thedehydrochlorination zone, as a result of the chlorinating ability of themelt, may be converted, in part or in total, to chlorinated product, asdescribed with reference to the chlorination zone (equations 1-7). Thechlorinated products produced from the ethane and/or ethylene or theethane and/or ethylene, itself is utilized for the production of vinylchloride by recycle of various components as hereinabove described.

The dichloroethane (primarily 1,2-dichloroethane) may also bedehydrochlorinated to vinyl chloride at dehydrochlorination temperaturesand pressures by any of the other procedures known in the art. Thus, forexample, the dichloroethane may be either thermally or catalyticallycracked to vinyl chloride as known in the art. The use of suchprocedures is well-known in the art and, accordingly, no furtherdescription thereof is deemed necessary for a full understanding of theinvention. In general, in such a system the ethane and/or ethylene isunchanged in passage through the dehydrochlorination zone.

The chlorination and dehydrochlorination in the presence of a melt aregenerally operated at temperatures from about 700° to about 1200°F.,preferably from about 750° to about 1000°F., although the temperaturesmay be as low as 575°F., and at pressures from about 1 to about 20atmospheres. The contacting of the feed and melt is generally effectedin a countercurrent fashion preferably with the feed as a continuousvapor phase, at residence times from about 1 to about 60 secondsalthough longer residence times may be employed. In the embodiments ofthe invention wherein the melt is previously contacted with oxygen, in aseparate reaction zone, such contacting is generally effected attemperatures from about 600° to about 900°F., although highertemperatures may be employed. The preferred operating temperatures forthe oxidation of the melt are from about 750° to about 870°F.

It should be apparent from the hereinabove noted reaction sequences,that the melt containing the multivalent metal chloride in some cases,participates in the reaction sequence and accordingly, does not behaveonly as a catalyst. Thus, for example, in the preferred embodiments ofthe invention, the melt functions to transfer oxygen, and as should beapparent from hereinabove noted equations, sufficient oxychloride mustbe produced to provide the oxygen requirements for the reactions, suchrequirements being greater for ethane as compared to ethylene andgreater for hydrogen chloride as compared to chlorine. In general, theoxychloride content of the molten mixture introduced into thechlorination reactor ranges from about 0.5 to about 5.5% and preferablyfrom about 1 to about 3%, all by weight, of the melt.

The melt, in addition to functioning as a reactant and/or catalyst is atemperature regulator. Thus, the circulating melt has a high heatabsorption capacity, thereby preventing runaway reaction during theexothermic chlorination and oxygen-contacting steps. The absorbed heatof reaction may be employed to both heat the various reactants toreaction temperature and supply heat for the endothermicdehydrochlorination. It should be apparent, however, that if additionalheating or cooling is required such heating or cooling may be suppliedfrom an external source. It should also be apparent that the heatabsorption capacity of the melt functions to limit temperaturevariations, i.e., temperature gradients, during the reactions.

Thus, as should be apparent from the hereinabove description of thepresent invention, vinyl chloride and dichloroethane may be producedfrom ethane and/or ethylene by contacting thereof with a melt containinga multivalent metal chloride in both its higher ane lower valence state,in the absence or presence of chlorine and/or hydrogen chloride, and inthe absence or presence of the corresponding oxychloride, preferably inthe presence of chlorine and/or hydrogen chloride and in the presence ofthe oxychloride. The 1,2-dichloroethane produced in the chlorination isseparated from heavier chlorinated components by use of a stripping gascontaining ethane and/or ethylene with the stripped 1,2-dichloroethane,including ethane and/or ethylene, being dehydrochlorinated to vinylchloride, preferably by direct contact with a melt containing amultivalent metal chloride in its higher and lower valence state. Theethane and/or ethylene used as stripping gas is also employed for theultimate production of vinyl chloride. The chlorination anddehydrochlorination as hereinafter described, are preferably effected byusing the same circulating melt, but it should be readily apparent thateach of the two steps could be effected with molten mixtures havingdifferent multivalent metal chlorides. Similarly, melts of identicalcompositions could be employed in each of the steps, without circulatingsuch identical melts between the two steps.

In accordance with a preferred embodiment of the invention, vinylchloride is produced from a net feed of ethane, molecular oxygen andchlorine and/or hydrogen chloride, using copper chlorides as the moltensalt mixture, with the intermediate products produced during thereaction being effectively converted to vinyl chloride. In accordancewith this preferred embodiment, the use of ethane or a mixture ofethylene and ethane, as a stripping gas, for stripping1,2-dichloroethane from heavier components improves the overall process.

The molten salt mixture, preferably containing from about 20 to about40% potassium chloride, as a melting point depressant, with theremainder being copper chlorides, all by weight, is contacted in a firstreaction zone with molecular oxygen to produce copper oxychloride. Thecupric chloride content of the melt is generally at least about 16%, byweight, of the melt, and generally from about 18% to about 50%, byweight, in order to provide sufficient cupric chloride for thesubsequent chlorination and dehydrochlorination reactions. It is to beunderstood, however, that lower amounts of cupric chloride may also beemployed by increasing salt circulation rates and residence tims. As aresult of the various reactions which occur during the chlorination anddehydrochlorination steps, the cupric chloride content of the melt doesnot significantly vary through the various reactions zones. Themolecular oxygen is preferably introduced in an amount, and at a rate,to provide a molten salt mixture containing from about 0.5 to about5.5%, preferably from about 1 to about 3%, all by weight, of copperoxychloride. It is to be understood that minor amounts of chlorineand/or hydrogen chloride could also be introduced into the firstreaction zone, but in accordance with this preferred embodiment, themajor portion of the chlorine and/or hydrogen chloride is added to thechlorination zone.

The molten salt mixture, now containing copper oxychloride, iscirculated to a second reaction zone (chlorination zone) wherein themolten salt is contacted with ethane and chlorine and/or hydrogenchloride as fresh feed and recycle ethyl chloride. The recycle may alsoinclude unconverted ethane and ethylene reaction intermediate. Therecycle, as hereinaftter described, may also include 1,1-dichloroethane.The chlorine, if used, is added in amounts which approximatestoichiometric quantities in order to eliminate the presence of chlorinein the reaction effluent, thereby also eliminating the necessity forchlorine recovery and recycle. The reactions which occur in thechlorination zone are believed to be best represented by hereinaboveequation (1)-(7) and (9). Thus, fresh ethane and chlorine and/orhydrogen chloride feed are converted to ethyl chloride, ethylene,dichloroethane (both 1,1-dichloroethane and 1,2-dichloroethane,primarily 1,2-dichloroethane) and vinyl chloride, with the recycle ethylchloride, ethylene, (if any), 1,1-dichloroethane also being ultimatelyconverted to vinyl chloride. The hydrogen chloride generated, in situ,reacts with the copper oxychloride of the melt to produce cupricchloride. In most cases, 100% conversion of the generated hydrogenchloride is not achieved and, accordingly, the reaction effluent mayalso include some hydrogen chloride. The chlorination reaction effluentwithdrawn from the chlorination zone includes, in addition tounconverted ethane, ethylene, ethyl chloride, dichloroethane,dichloroethylene, hydrogen chloride (if any) water vapor and vinylchloride. The chlorination reaction effluent further includes minorportions of one or more of the following: trichloroethylene,tetrachloroethylene, trichloroethanes, and tetrachloroethanes.

The chlorination reaction effluent is passed to a separation andrecovery zone wherein ethane and ethylene are recovered as a lightstream, vinyl chloride is recovered as product, ethyl chloride isrecovered as recycle for the chlorination zone. A stream comprised of1,2-dichloroethane and heavier chlorinated hydrocarbons is thenintroduced into a stripping zone to strip the 1,2-dichloroethane fromthe heavier hydrocarbons, using as a stripping gas, either a portion ofthe ethane to be used as fresh feed or all or a portion of the mixtureof ethane and ethylene recovered from the chlorination effluent. Themixed ethane-ethylene stream, recovered from the effluent and not usedas stripping gas is recycled to the chlorination zone.

In general, the chlorination reaction effluent also includes1,1-dichloroethane, which is preferably recovered separately from the1,2-dichloroethane, i.e, with the ethyl chloride, and recycle to thechlorination zone for dehydrochlorination to vinyl chloride. It is to beunderstood, however, that the 1,1-dichloroethane could be recovered withthe 1,2-dichloroethane overhead in the heavy ends column anddehydrochlorinated with the 1,2-dichloroethane in the separatedehydrochlorination zone.

The 1,2-dichloroethane, including ethane or a mixture of ethane andethylene is introduced into the dehydrochlorination zone and contactedtherein with the molten salt from either the first reaction zone, thesecond reaction zone (chlorination zone), or molten salt from bothzones, preferably from the first reaction zone whereby the melt includesoxychloride, to effect dehydrochlorination of the 1,2-dichloroethane tovinyl chloride. The reaction effluent includes vinyl chloride, anyunconverted 1,2-dichloroethane, and chlorinated hydrocarbons producedfrom the ethane or mixture of ethane and ethylene introduced with the1,2-dichloroethane. In addition, if the melt employed in thedehydrochlorination zone is obtained from the second reaction zone, thedehydrochlorination reaction effluent includes hydrogen chloride, and ifthe melt is obtained from the first reaction zone, the effluent includeswater vapor and any hydrogen chloride which does not react with thecopper oxychloride present in the melt. The dehydrochlorination reactioneffluent is introduced into a separation and recovery zone to recoverthe various components, with vinyl chloride being recovered as reactionproduct, hydrogen chloride, if any, being recycled to the chlorinationzone, and unconverted 1,2-dichloroethane being recycled to thedehydrochlorination zone.

The heavier chlorinated hydrocarbons separated from 1,2-dichloroethaneare preferably burned to recover chlorine values which are recycled tothe melt oxidation zone.

The molten salt to feed weight ratio (based on total feed to thechlorination reaction zone) is preferably from about 25:1 to about200:1, with the molten salt, at such high salt circulation rates, actingas a heat sink, whereby there is little temperature variation betweenthe various zones; i.e., in general the temperature fluctuation betweenthe various zones is no greater than about 130°F. and generally fromabout 15° to about 50°F.

It should be readily apparent that in accordance with the preferredembodiment, vinyl chloride is effectively produced from ethane, chlorineand/or hydrogen chloride and oxygen as a result of the recycle ofessentially all reaction intermediates, with the overall reaction beingrepresented by equations (10) and/or (11).

It is also to be understood that the preferred ethane feed could alsocontain some ethylene, and/or propane and/or methane as for example, inthe case where a C₂ stream is recovered from a refinery.

The invention will now be further described with reference toembodiments thereof illustrated in the accompanying drawings wherein:

FIG. 1 is a simplified schematic process flow diagram of the reactionportion of an embodiment of the invention; and

FIG. 2 is a simplified schematic process flow diagram of the separationand recovery portion for recovery reaction products.

It is to be understood that the molten copper chloride salts are highlycorrosive and, accordingly, the processing equipment must be suitablyprotected; e.g., the reactors may be lined with ceramic. Similarly, ifpumps are used for transporting the molten salts they must also beprotected. The molten salts, however, are preferably transferred betweenthe reactors and by the use of gas lifts, as known in the art.

Referring now to FIG. 1, a molten chloride salt, such as a mixture ofpotassium chloride, cuprous chloride and cupric chloride in line 10 isintroduced into the top of the reaction portion of an oxidation vessel11 maintained, as hereinabove described, at temperatures and pressuresuitable for oxidizing the molten salts. A compressed oxygen-containinggas, such as air, in line 12 is introduced into the bottom of vessel 11and is passed in countercurrent contact to the descending molten salt,resulting in oxidation of the salt to produce copper oxychloride withthe concurrent evolution of heat. In addition, a combustion effluentresulting from the combustion of heavier chlorinated by products, suchas tri- and tetrachloroethanes and ethylenes and including hydrogenchloride and/or chlorine is introduced into vessel 11 through line 12a,as described in British patent and specification No. 1,205,831.

An effluent gas, comprised essentially of the nitrogen introduced withthe air, (the effluent would also include combustion products, if acombustion effluent is introduced through line 12a) rises into the topof the vessel 11 wherein the effluent gas is combined with lift gas, ashereinafter described, introduced through line 13. The effluent gas isdirectly contacted in the top of vessel 11 with a spray of quenchliquid, in particular aqueous hydrogen chloride introduced through line14 to cool the effluent gas and thereby eliminate any vaporized andentrained salts therefrom. The effluent gas, now containing vaporizedquench liquid, is withdrawn from vessel 11 through line 15 andintroduced into a direct contact quench tower 16, of a type known in theart wherein the effluent gas is cooled by direct contact with a suitablequench liquid, in particular aqueous hydrogen chloride, introducedthrough line 17 to thereby remove vaporized quench liquid from theeffluent gas.

The quench liquid is withdrawn from the bottom of tower 16 through line18 and a first portion passed through line 14 for quenching the effluentgas in vessel 11. A second portion of the quench liquid is passedthrough line 19, containing a cooler 21, for introduction into thequench tower 16 through 17.

An effluent gas, comprised essentially of nitrogen, is withdrawn fromquench tower 16 throughline 22 and a portion thereof purged through line23. The remaining portion of the nitrogen effluent gas is compressed incompressor 24 and the temperature thereof regulated in heat exchanger 63prior to passage through lines 25 and 26 for use as a lift gas fortransporting molten salt, as hereinafter described.

The molten salt, now containing copper oxychloride, is withdrawn fromthe bottom of vessel 11 through line 31 and lifted by the lift gas inline 25 into a separation vessel 32 positioned adjacent the top of thereaction portion of a reaction vessel 33. In separator 32, the moltensalt is separated from the lift gas, witht the separated lift gas beingwithdrawn through line 35 and combined with lift gas from the oxidationreactor for introduction into the quenching portion of vessel 11 throughline 13.

The reaction vessel 33 is divided into two separate reaction sections,41 and 42 with reaction section 41 functioning as a chlorinationreaction zone and section 42 as a dehydrochlorination reaction zone. Themolten salt, containing cuprous chloride, cupric chloride, copperoxychloride and the potassium chloride melting point depressant, fromseparator 32, in line 34, is introduced into both reaction sections 41and 42.

Fresh feed chlorine and/or hydrogen chloride is introduced into thebottom of section 41 through 43 and all or a portion of fresh feedethane and/or ethylene, preferably ethane, in line 44 is combined with arecycle chlorinated hydrocarbon stream comprised of ethyl chloride andalso some dichloroethylene and 1,1-dichloroethane, in line 45, andrecycle ethane and ethylene (if any) in line 46, for introduction intothe bottom of section 41 through line 47. It is to be understood thatthe various streams could be separately introduced.

The reaction section 41 is operated at the temperatures and pressureshereinabove described, to produce an effluent which contains, ascombined reaction product, vinyl chloride and 1,2-dichloroethane. Theeffluent also includes ethyl chloride, some 1,1-dichloroethane,dichloroethylenes, ethane, ethylene, water vapor, some hydrogen chlorideand heavier chlorinated hydrocarbons.

1,2-dichloroethane, including ethane and/or ethylene in line 51 isintroduced into the bottom of reaction section 42 and countercurrentlycontacts the descending molten salt. As a result of such contact, the1,2-dichloroethane is dehydrochlorinated to vinyl chloride, and hydrogenchloride, which as hereinabove noted, reacts with the oxychloridepresent in the melt. In addition, some or all of the ethane and/orethylene is chlorinated as a result of contact with the melt.

It is to be understood, that the dehydrochlorination reaction may alsobe effected in a separate vessel instead of in a separate section ofvessel 33.

The reaction effluent from chlorination section 41 is combined with thereaction effluent from dehydrochlorination reaction section 42 inquenching section 52 wherein the effluent gas is directly contacted witha spray of quench liquid, in particular one or more of the chlorinatedhydrocarbons produced in reaction section 41, introduced through line 53to cool the effluent gas and thereby eliminate vaporized and entrainedsalts therefrom.

The effluent gas, now containing vaporized quench liquid, is withdrawnfrom vessel 33 through line 54 and introduced into a separation andrecovery section (FIG. 2) for recovery of the various components.

A molten salt obtained from sections 41 and 42 is withdrawn from thebottom of reactor 33 through line 61 and lifted by lift gas in line 26into a separation vessel 62 positioned adjacent the top of reactor 11.In separator 62 the molten salt is separated from the lift gas andintroduced through line 10 into vessel 11. The lift gas is withdrawnfrom separator 62 through line 64 and combined with the lift gas in line35 for introduction into the top quenching section of vessel 11 throughline 13.

Referring now to FIG. 2, the reaction effluent in line 54 is cooled incondenser 110, primarily to condense a portion of the water therefrom(the condensed water would also contain hydrogen chloride, if present),the aforesaid cooling also resulting in the condensation of chlorinatedhydrocarbons, including the chlorinated hydrocarbons used as quenchliquid. The condensed water and chlorinated hydrocarbons are separatedin a separator III, with a water phase being withdrawn through line 113.A portion of the chlorinated hydrocarbons in line 113 is recycledthrough line 53 as quench liquid for reactor 33. Alternatively, all ofsuch chlorinated hydrocarbons, if required, may be recycled as quenchliquid. The water phase in line 112 is stripped of entrained anddissolved chlorinated hydrocarbon in a stripping column (not shown) andthe recovered chlorinated hydrocarbons (from the stripping column) inline 112a are combined with the chlorinated hydrocarbons in line 113.Depending on the amount of hydrogen chloride present in the water, thewater may also be treated to recover hydrogen chloride or a concentratedsolution of hydrogen chloride.

The remaining portion of the gaseous effluent in line 114 is optionallypassed through an alkali scrubbing zone, of a type known in the art,schematically indicated as 115, to remove any remaining hydrogenchloride therefrom.

The gaseous effluent from the alkali scrubbing zone 115, if used, inline 116 is generally passed through a further cooling and separationzone, schematically indicated as 117, to condense further water andchlorinated hydrocarbons therefrom; an acid gas removal zone 118, of atype known in the art, to remove any acid gas, primarily carbon dioxide,and a drier 119, and introduced into a fractional distillation column121. The chlorinated hydrocarbons in line 113 and chlorinatedhydrocarbons separated in zone 117 are combined and dried in drier 120for introduction into column 121. Alternatively, if required, a portionof the chlorinated hydrocarbons recovered in zone 117 may be recycled asquench liquid to reactor 33. The water separated in zone 117 may bepassed to a stripping column to recover any chlorinated hydrocarbonswith such recovered chlorinated hydrocarbons also being introduced intocolumn 121.

The column 121 is operated at temperatures and pressures to produce agaseous overhead comprised of ethane and ethylene, which is recovered inline 133. All or a portion or none of the ethane-ethylene stream in line133 may be used as a stripping gas in line 134, with the remainder, ifany, being recycled to reactor 33 through line 46.

A chlorinated hydrocarbon bottoms withdrawn from column 121 through line122 is introduced into a fractional distillation column 123 operated attemperatures and pressures to produced an overhead primarily comprisedof vinyl chloride which is recovered through line 124.

A chlorinated hydrocarbon bottoms withdrawn from column 123 through line125 is introduced into a fractional distillation column 126 operated attemperatures and pressures to recover as overhead 1,1-dichloroethane andlower boiling chlorinated hydrocarbons, in particular ethyl chloride anddichloroethylenes. The overhead from column 126, comprised essentiallyof 1,1-dichloroethane, dichloroethylenes and ethyl chloride is recoveredin line 45 for recycle to reactor 33. If desired, the overhead fromcolumn 126 may be further fractionated to produce a recycle streamessentially free of dichloroethylenes. As a further alternative, column126 may be operated to recover ethyl chloride as overhead in which caseany 1,1-dichloroethane and dichloroethylenes will be ultimatelyrecovered with the stripped 1,2-dichloroethane.

A bottoms of 1,2-dichloroethane and heavier chlorinated products iswithdrawn from column 126 through line 127 and introduced into the topof stripping column 28. The stripping gas in line 136, which may beeither ethane and/or ethylene fresh feed, provided through line 137, orethane and ethylene recovered from the chlorination effluent in line 134or a combination of both, is introduced into the bottom reboiler 138 toreduced the partial pressure over the heavy residue in the reboiler andthereby reduce the boiling point of the residue in the reboiler. Thestripper is operated, as hereinabove described, to recover1,2-dichloroethane and ethane and/or ethylene, as overhead product inline 51, for introduction into the dehydrochlorination section 42 ofreactor 33. The stripper is also preferably provided with a sidereboiler 140.

The bottoms from column 128, comprised of chlorinated hydrocarbonsheavier than 1,2-dichloroethane in line 139 is introduced into acombustion zone 141 along with oxygen wherein the chlorinatedhydrocarbons are burned to produce a combustion effluent, including thechlorine values of the chlorinated hydrocarbon as chlorine and/orhydrogen chloride. The combustion effluent from combustion zone 141 isintroduced into oxidizer 11 through line 12a.

It is to be understood that although the present invention has beendescribed with respect to the preferred embodiment in which ethaneand/or ethylene are chlorinated by the use of molten salts the presentinvention is also applicable to other processes for chlorinating (theterm chlorinating is used in a generic sense and also includes so called"oxychlorination" processes) ethane and/or ethylene to produce vinylchloride; i.e., the heavy ends recovered from such a process including1,2-dichloroethane and heavier components is introduced into a strippingzone wherein 1,2-dichloroethane is stripped from heavier chlorinatedcomponents by use of ethane and/or ethylene (either recycle or freshfeed). Thud, the effluent obtained by the chlorination and/oroxychlorination of ethane and/or ethylene includes 1,2-dichloroethaneand heavier components, and 1,2-dichloroethane is separated from suchheavier components by the use of ethane and/or ethylene, as a strippinggas, with the stripped 1,2-dichloroethane, including stripping gas,being introduced into a dehydrochlorination reaction zone. Thedehydrochlorination effluent is then treated to recover variouscomponents whereby the ethane and/or ethylene used stripping gas iseventually employed for the production of vinyl chloride.

The invention will be further described with respect to the followingexample, but the scope of the invention is not to be limited thereby.

EXAMPLE

The feed in line 127, comprised of 60 weight percent 1,2-dichloroethaneis introduced into column 128 at a temperature of 320°F. The column isoperated at a pressure of 70 psig, an overhead temperature of 300°F, abottoms temperature of 275°F and a side reboiler temperature of 340°F.Fresh feed ethane is introduced into the bottoms reboiler to provide amole ratio of ethane to vapor generated in the reboiler of 1.5:1.

The heavy residue contains no more than 1 weight percent1,2-dichloroethane.

The present invention is advantageous in that loss of 1,2-dichloroethanein the heavier chlorinated residuum is minimized; i.e., by proceeding inaccordance with the present invention the 1,2-dichloroethane content ofthe heavier chlorinated residuum can be reduced to 1 weight percent andless. Furthermore, the above is effectively accomplished without theintroduction of extraneous components into the process, with thestripping gas being ultimately converted to final product.

Numerous modifications and variations of the present invention arepossible in light of the above teachings and, therefore, within thescope of the appended claims the invention may be practiced otherwisethan as particularly described.

WHAT IS CLAIMED IS:
 1. A process for recovering 1,2-dichloroethane froma mixture of 1,2-dichloroethane and at least one chlorinated hydrocarbonheavier than 1,2-dichloroethane selected from the group consisting oftrichloroethane, tetrachloroethane, tetrachloroethylene,trichloroethylene, chlorinated butanes and chlorinated butenes,comprising:introducing said mixture into a stripping column operated atan overhead temperature from about 225° to about 350°F, a bottomstemperature from about 270° to about 410°F and a pressure from about 20psig to about 130 psig to separate and recover 1,2-dichloroethane fromthe mixture as overhead; introducing into the bottoms of said strippingcolumn, as stripping gas, a member selected from the group consisting ofethane, ethylene and mixtures of ethane and ethylene to strip1,2-dichloroethane from said mixture, said stripping gas beingintroduced in a molar amount sufficient to reduce the partial pressureof 1,2-dichloroethane over the heavier chlorinated hydrocarbons andprovide a bottoms containing no greater than 1 wt.% of1,2-dichloroethane; recovering as overhead from said stripping column1,2-dichloroethane and said stripping gas; and recovering a bottoms fromthe stripping column having a 1,2-dichloroethane content of no greaterthan 1 wt. %.
 2. The process of claim 1 wherein the stripping columnincludes a bottoms reboiler and the stripping gas is introduced into thebottoms of the stripping column through the bottoms reboiler.
 3. Theprocess of claim 1 wherein the stripping gas is employed in an amount toprovide a mole ratio of stripping gas to vapor generated in the bottomsreboiler of from 0.5:1 to 1.5:1.